Redundancy technologies in which communication is performed using a plurality of communication lines are used. As one of the redundancy technologies, an aggregation technology is known. The aggregation can secure a wide communication band and can improve the reliability by aggregating a plurality of communication lines into one communication line. Here, all of technologies for aggregating a plurality of communication lines into one communication line are referred to as aggregations. As related literature of aggregations, PTL 1 is known, for example.
In the meanwhile, as a standard for synchronizing times between a plurality of communication apparatuses, IEEE1588 (Precision Time Protocol: PTP) is known. In IEEE1588, a PTP packet in which a clock time of the own apparatus is written is transmitted/received, so that time synchronization between communication apparatuses becomes possible. As related literature of time synchronization by IEEE1588, PTL 2 is known, for example.